Antijackknifing system

ABSTRACT

An antijackknifing system for a tractor-semitrailer combination. In one embodiment, a first fluid cylinder is provided having a piston with fluid on opposite sides thereof, the piston being linearly actuated in opposite directions, respectively, by turning movement of the steerable front wheels of the tractor in opposite directions from the center position. A second fluid cylinder is provided having a piston therein with fluid on opposite sides thereof, the piston being linearly actuated in opposite directions from a neutral position, respectively, by pivotal turning movement of the semitrailer with respect to the tractor in opposite directions from its centered position. A third fluid cylinder is provided having a piston with fluid on opposite sides thereof. A first conduit connects the three cylinders on one side of the respective pistons thereby providing a first closed fluid system, and a second conduit connects the three cylinders on the opposite sides of the respective pistons thereby providing a second closed fluid system so that movement of the piston of one of the first and second cylinders away from its neutral position without corresponding coordinated movement of the piston of the other of the first and second cylinders causes movement of the piston of the third cylinder away from its neutral position to accommodate fluid displaced by movement of the piston of the one cylinder. The piston of the third cylinder is coupled to increase the braking force exerted by the trailer brakes and simultaneously to decrease the braking force exerted by the tractor brakes in response to movement of the piston of the third cylinder away from its neutral position in either direction thereby to assist the driver in restoring a normal coordinated relationship between the position of the front wheels of the tractor and the pivotal position of the semitrailer with respect to the tractor.

United States Patent [72] Inventor Harry D. Forse 220 Woods Road,Edgewood Addition,

Anderson, Ind. 40611 [21] App]v No. 883,826 [22] Filed Dec. 10, 1969[45] Patented Nov. 9, 1971 [54] ANTIJACKKNIFING SYSTEM 16 Claims, 8Drawing Figs.

Primary Examiner- Leo Friaglia Attorney-Hood, Gust, Irish & LundyABSTRACT: An antijackknifing system for a tractorsemitrailercombination. in one embodiment, a first fluid cylinder is providedhaving a piston with .fluid on opposite sides thereof, the piston beinglinearly actuated in opposite directions, respectively, by turningmovement of the steerable front wheels of the tractor in oppositedirections from the center position. A second fluid cylinder is providedhaving a piston therein with fluid on opposite sides thereof, the pistonbeing linearly actuated in opposite directions from a neutral position,respectively, by pivotal turning movement of the semitrailer withrespect to the tractor in opposite directions from its centeredposition. A third fluid cylinder is provided having a piston with fluidon opposite sides thereof. A first conduit connects the three cylinderson one side ofthe respective pistons thereby providing a first closedfluid system, and a second conduit connects the three cylinders on theopposite sides of the respective pistons thereby providing a secondclosed fluid system so that movement of the piston of one of the firstand second cylinders away from its neutral position withoutcorresponding coordinated movement of the piston of the other of thefirst and second cylinders causes movement of the piston of the thirdcylinder away from its neutral position to accommodate fluid displacedby movement of the piston of the one cylinder. The piston of the thirdcylinder is coupled to increase the braking force exerted by the trailerbrakes and simultaneously to decrease the braking force exerted by thetractor brakes in response to movement of the piston of the thirdcylinder away from its neutral position in either direction thereby toassist the driver in restoring a normal coordinated relationship betweenthe position of the front wheels of the tractor and the pivotal positionof the semitrailer with respect 9 to the tractor.

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INVENTORZ HARRY D.Fonss,

BY I I L ANTIJACKKNIFING SYSTEM BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates generally to tractor-semitrailercombinations, and more particularly to an antijackknifing system for usewith such combinations.

2. Description of the Prior Art Conventional tractor-semitrailercombinations comprise a wheeled tractor or towing vehicle which hasselectively actuable wheel brakes and steerable front wheels, and awheeled semitrailer vehicle which has selectively actuable wheel brakes,the semitrailer being pivotally connected adjacent its forward end tothe tractor adjacent its rear end by a so-called fifth" wheel. Means areconventionally provided for normally selectively applying both thetractor and semitrailer brakes.

In normal operation of said tractor-semitrailer combination on ahighway, the position of the front wheels and the pivotal position ofthe semitrailer with respect to the tractor is coordinated in trainfashion. Thus, on a straight section of highway, the steerable frontwheels of the tractor are centered and the semitrailer follows behind ina centered position with respect to the tractor. Further, in negotiatinga normal turn in either direction, the steerable front wheels of thetractor will be turned in one direction away from the centered position,such as toward the right, and the semitrailer will be pivoted withrespect to the tractor away from its centered position in the samedirection, i.e., toward the right, the front wheels of the tractor andthe trailer wheels thus being respectively positioned for making acoordinated turn.

By reason of the ability of the semitrailer to pivot with respect to thetractor, there is an ever-present hazard of the semitrailer skidding toone side or the other with respect to the tractor resulting in asituation commonly referred to as jackknifmg." Such jackknifing may becaused by a variety of conditions such as sudden application of thebrakes or a steep descent so that the semitrailer tends to override thetractor, slippery road conditions, or the driver making a sudden turn.Once such jackknifing has commenced, it is often very difficult to stopand frequently results in complete loss of control of the vehicle and aresulting accident.

Various systems and devices have been proposed for eliminating orcorrecting jackknifing. One simple prior system merely provides fixedstops which limit the pivotal movement of the semitrailer with respectto the tractor. This arrangement, however, restricts maneuverability ofthe vehicle, such as when hacking into a loading dock. Another priorsystem actuates the trailer brakes in response to a predeterminedangular position of the semitrailer with respect to the tractor. Yetanother prior system incorporates a brake associated with the fifthwheel which is actuated in response to a tendency for the semitrailer tooverride the tractor, or in response to a predetermined angular positionof the semitrailer with respect to the tractor. Yet another prior systemactuates the trailer brakes in response to centrifugal force due toskidding motion of the semitrailer. In still another prior system, forceis applied to the fifth wheel mechanism in a direction to straighten thesemitrailer with respect to the tractor.

Certain of the above-mentioned prior antijackknifing systems haverequired that not only the tractor, but also the trailer be speciallymodified. In the design of an antijackknifing system, it is particularlydesirable that the additional apparatus required in the system beconfined to the tractor to the end that any conventional semitrailer maybe towed thereby. Further, since jackknifing generally occurs veryrapidly, it is also highly desirable that the antijackknifing system beautomatically actuated immediately upon the beginning of jackknifing.

SUMMARY OF THE INVENTION The present invention operates on the premisethat in normal operation of a tractorsemitrailer combination, theabovedescribed coordinated relationship exists between the front wheelsof the tractor and the semitrailer, jackknifing being evidenced by anuncoordinated turning movement of the semitrailer with respect to thefront wheels. Further, jackknifing is known to occur by reason of theapplication of excessive braking force by the tractor brakes and/orinsufficient braking force by the trailer brakes. Thus, in accordancewith the invention, the braking effort applied by the tractor brakes isdecreased and/or the braking effort applied by the trailer brakes isincreased in response to the sensing of uncoordinated turning movementof the semitrailer with respect to the front wheels of the tractor.

The invention, in its broader aspects, therefore provides means forsensing the absence of a normal, coordinated relationship between theposition of the front wheels of the tractor and the pivotal position ofthe semitrailer with respect to the tractor, and means for modifying thebraking effort applied by at least one of the tractor and semitrailerbrakes in response to the sensing means.

It is accordingly an object of the present invention to provide animproved antijackknifing system for use with a tractorsemitrailercombination.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates oneembodiment of the invention with the front wheels of the tractor and thetrailer positioned for a normal, coordinated turn;

FIG. 2 is a schematic view similar to FIG. 1 showing the operation ofthe system during the beginning of jackknifing;

FIG. 3 is a schematic illustration similar to FIGS. 1 and 2 showing thesystem in a full jackknife situation;

FIG. 4 is a fragmentary side view, partly in cross section, illustratinga fifth wheel mechanism usable with the embodiment of the previousfigures;

FIG. 5 is a top cross-sectional view taken generally along the line 5-5of FIG. 4;

FIG. 6 is a top cross-sectional view taken generally along the line 6-6of FIG. 4;

FIG. 7 is a schematic illustration of an airbrake system usable inconjunction with the antijackknifing system of the previous figures; and

FIG. 8 is a schematic illustration showing another embodiment of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 of thedrawings, a conventional tractor is designated by the dashed-line box 10and a conventional semitrailer is designated by the dashed-line box 12,trailer 12 being pivotally connected adjacent its forward end to tractor10 adjacent its rear end, as at 14, by a fifth wheel mechanism, such asthat described below in conjunction with FIGS. 4, 5 and 6. Tractor 10includes front wheels 16 which are steerable by a conventional steeringwheel, shown by the dashed lines 18, through a conventional steeringlinkage indicated at 20. The steerable front wheels 16 and the rearwheels (not shown) of the tractor are provided with conventional brakesshown schematically at 22 in FIG. 7. Semitrailer 12 is provided withwheels 24 which are also provided with conventional brakes 26 as shownschematically in FIG. 7.

In accordance with the invention, an antijackknifing system 28 isprovided mounted on the tractor l0. Antijackknifing system 28 comprisesa first pair of fluid cylinders 30 and 32, respectively having pistons34, 36 therein. Pistons 34, 36 respectively have piston rods 38, 40associated therewith which, in the illustrated embodiment, are connectedby a rack 42, pistons 34, 36 of cylinders 30, 32 thus moving in unison.

Rack 42 is moved linearly and in opposite directions, as shown by arrow44, by a suitable gear 46 coupled to the steering shaft 48. Pistons 34,36 have a neutral position generally midway between the opposite ends ofthe respective cylinders 30, 32 as shown by the dashed lines 34a, 36a,when the steerable front wheels 16 are centered as shown by the dashedlines 16a. Thus, when front wheels 16 are turned toward the right, asshown in solid lines in FIG. 1, gear 46 will drive rack 42 so as to movepistons 34, 36 toward the left ends of cylinders 30, 32, respectively,as shown in solid lines. Similarly, turning of front wheels 16 towardthe left away from the centered position 16a will cause gear 46 to driverack 42 toward the right thereby linearly to move pistons 34, 36 awayfrom their neutral positions 34a, 36a toward the right ends of cylinders30, 32, respectively.

A second pair of fluid cylinders 50, 52, is provided respectively havingpistons 54, 56 therein. Pistons 54, 56 respectively have piston rods 58,60 extending outwardly from the respective cylinders 50, 52 andconnected by rack 62 so that pistons 54, 56 are simultaneously moved.Rack 52 is driven by a suitable gear 64 attached to the fifth wheelmechanism (FIGS. 4 and so as to rotate with pivotal movement of trailer12 with respect to tractor 10. With trailer 12 centered with respect totractor 10, as shown by the dashed lines at 120, pistons 54, 56 are inneutral positions generally midway between the opposite ends of therespective cylinders 50, 52 as shown by the dashed lines at 54a, 56a.With trailer 12 pivoted toward the right, as shown in FIG. 1, thusmaking a coordinated turn with the front wheels 16, gear 64 drives rack62 and pistons 54, 56 toward the left ends of cylinders 50, 52, as shownin solid lines in FIG. 1. Similarly, when trailer 12 pivots toward theleft from its centered position, gear 64 drives rack 62 toward the rightthereby linearly to move pistons 54, 56 from their neutral positions54a, 56a toward the right ends of cylinders 50, 52.

A third pair of cylinders 66, 68 is provided respectively having pistons70, 72 therein. in the illustrated embodiment, cylinder 66 is of thefree piston type, i.e., its piston 70 does not actuate, nor is itactuated by any external mechanism. Piston rod 74 is connected to piston72 and actuates antijackknife pilot valve 76 (FIG. 7). Spring 78 incylinder 66 urges free piston 70 toward end 80 of cylinder 66, whilespring 82 in cylinder 68 urges piston 72 toward end 84 of cylinder 68.

A first fluid conduit 86 is connected to end 88 of cylinder 30, end 80of cylinder 66, and end 90 of cylinder 52, while a second fluid conduit92 is connected to ends 94 of cylinder 32, end 84 of cylinder 68 and end96 of cylinder 50. Space 98 between piston 34 and end 88 of cylinder 30,space 100 between end 80 and piston 70 of cylinder 66, and space 102between end 90 and piston 56 of cylinder 52 together with conduit 86 arefilled with suitable hydraulic fluid, thus forming a closed fluidsystem. Similarly, space 104 between end 94 and piston 36 of cylinder32, space 106 between end 84 and piston 72 of cylinder 68, and space 108between end 96 and piston 54 of cylinder 50, together with conduit 92,are filled with suitable hydraulic fluid, thereby forming a secondclosed fluid system.

Cylinders 30, 32, 50 and 52 each have generally the same volume, whilecylinders 66 and 68 each have an effective volume generally twice thatof cylinders 30, 32, 50 and 52. The volume of the hydraulic fluid ineach of the two closed fluid systems is substantially the same. Assumingnow that front wheels 16 and semitrailer 12 are respectively centered,as shown in dashed lines at 16a, 12a, with pistons 34, 36, 54 and 56thus at their neutral positions as shown in dashed lines at 34a, 36a,54a, and 560, the volume of the fluid in the two closed fluid systems issuch that pistons 70, 72 of cylinders 66, 68, which serve as accumulatorcylinders, will likewise be at neutral positions, as shown in solidlines in FIG. 1. Assuming further that the tractor-semitrailer is makinga coordinated turn to the right with front wheels 16 turned to the rightand semitrailer 12 pivoted to the right, as shown in FIG. 1, with theposition of front wheels 16 and the pivotal position of semitrailer 12being properly coordinated, pistons 34, 36 will be moved in unison bygear 46 toward ends 88, 110 of cylinders 30, 32, and pistons 54, 56 willsimilarly be moved in unison by gear 64 the same distance toward ends96, 112, as shown in FIG. 1. With the turning movement of front wheels16 and semitrailer 12 being coordinated, the fluid in space 98 ofcylinder 30 displaced by movement of piston 34 toward end 88 will betransferred by conduit 86 into and accommodated in end space 102 ofcylinder 52 by reason of the corresponding movement of piston 56 towardend 112. Similarly, the fluid in space 108 of cylinder 50 displaced bymovement of piston 54 toward end 96 will be transferred by conduit 92into and accommodated in end space 104 of cylinder 32 by reason of thecorresponding movement of piston 36 toward end 110. Thus, the two closedfluid systems remain in a balanced condition, the volume of the fluid inspaces 100, 106 will remain the same, and there will be no movement ofpistons 70, 72 in the accumulator cylinders 66, 68. It will be observedthat springs 78, 82 which respectively urge pistons 70, 72 of cylinders66, 68 toward ends 80, 1 14 cooperate to tend to resist movement ofpistons 70, 72 when front wheels 16 are initially turned slightly toinitiate a coordinated turn.

It will now be seen that during any operation of the tractorsemitrailercombination in which the positions of the front wheels 16 and thesemitrailer 12 are coordinated, pistons 70, 72 of cylinders 66, 68 willremain in their neutral positions, and thus that the antijackknife pilotvalve 76 will not be actuated.

Suitable vent ports 116, 118, 120, 122, 124 and 126 are preferablyprovided for cylinders 30, 32, 66, 68, 50 and 52, as shown.

Referring now additionally to FIG. 2, it is assumed that thetractor-semitrailer combination was proceeding in a straight line withthe front wheels 16 and semitrailer 12 in their respective centeredpositions and in longitudinal alignment. Thus, pistons 34, 36, 54, 56,70 and 72 will be in their neutral positions, as described above.Assuming now that semitrailer 12 starts to jackknife toward the right,as shown by the arrow 126, pistons 54, 56 of cylinders 50, 52 will bemoved in unison toward ends 96, 112 of those cylinders, as shown by thearrow 128, pistons 34, 36 of cylinders 30, 32 momentarily remaining intheir initial neutral positions, since the driver has not yet attemptedto correct the jackknifing condition by turning the front wheels 16 ofthe tractor 10 in the opposite direction, i.e., toward the left.

It will now be seen that the fluid in space 108 of cylinder 15 displacedby movement of piston 54 toward end 96 cannot be accommodated in space104 of cylinder 32, to which cylinder 50 is connected by fluid conduit92, since piston 36 remains in its initial neutral position. Thus, thefluid displaced from space 108 is forced through fluid conduit 92 andinto space 106 of cylinder 68 causing piston 72 and piston rod 74 to bemoved toward the right against the force exerted by spring 82, as shownby arrow 130, the fluid displaced from space 108 of cylinder 50 thusbeing transferred into and accommodated in space 106 of cylinder 68 byreason of corresponding movement of piston 72 in direction 130. Thismovement of piston rod 74 in direction 130 begins to actuateantijackknife pilot valve 76.

It will be seen that the corresponding movement of piston 56 of cylinder52 in direction 128 increases the volume of space 102, there being nocorresponding decrease in the volume of space 98 of cylinder 30 sincepiston 34 has remained in its initial neutral position. Thus, spring 78in cylinder 66 forces piston 70 toward end in the direction shown by thearrow 132, thereby correspondingly to reduce the volume of space and todisplace fluid therein through fluid conduit 86 into space 102 ofcylinder 52.

As will hereinafter be more fully described in connection with FIG. 7 ofthe drawings, antijackknife pilot valve 76 is coupled in the brakingsystem of the tractor-semitrailer l0, l2 and its actuation, as abovedescribed, reduces the braking effort applied by the tractor brakes 22and increases thebraking effort applied by the trailer brakes 26,thereby to assist the driver in correcting the jackknifing condition. Itwill further be observed that by reason of the fact that the two closedfluid systems, above described, are respectively maintained in balancedcondition by springs 78, 82 in cylinders 66, 68, sudden, violent turningmotion of the front wheels 16, which can cause occurrence ofjackknifing, as above described, and also sudden jackknifing movement ofsemitrailer 12 is resisted, thus tending to prevent the occurrence ofjackknifing and/or additionally to prevent worsening of a jackknifingcondition.

Referring now additionally to FIG. 3, a full jackknife condition isshown in which the driver has now turned the front wheels 16 of tractortoward the left, as shown by the arrows 134 in an effort to correct thesituation. This left-turning movement of front wheels 16 results insimultaneous movement of pistons 34, 36 of cylinders 30, 32 toward theright, as shown by the arrow 138, toward cylinder ends 136, 94 thusreducing the volume of space 104 of cylinder 32 and increasing thevolume of space 98. Reduction of the volume of space 104 of cylinder 32by movement of piston 36 toward end 94 causes fluid to be displaced fromspace 104 through fluid conduit 88 and into space 106 of cylinder 68thereby further to move piston 72 in direction 130 against spring 82,thereby further to move piston rod 74 and further to actuateantijackknife pilot valve 76. It will be observed that a correspondingmovement of piston 34 of cylinder 30 toward end 136 has increased thevolume of space 98 of cylinder 30, and thus spring 78 of cylinder 66forces piston 70 further in direction 132 correspondingly to reduce thevolume of space 100 and to displace the fluid therefrom through fluidconduit 86 into space 98 of cylinder 30.

It will be observed that as spring 82 in cylinder 68 is progressivelycompressed by movement of piston 72 in direction 130, as abovedescribed, its resistive force progressively increases, thusprogressively resisting further jackknifing movement of semitrailer 12.

In the illustrated embodiment, antijackknife pilot valve 76 is of thetype which is actuated in response to movement of piston rod 74 ineither direction away from the neutral position of cylinder 72. Thus, itwill readily be seen that the system functions in the identical manner,with the positions of the pistons merely reversed, in the case of theoccurrence of jackknifing to the left, rather than to the right, asabove described. It will further be readily understood that rather thanproviding a double-acting antijackknifing pilot valve 76 actuated inresponse to movement of piston 72 of cylinder 68 in either directionaway from its neutral position, as above described, antijackknife pilotvalve 76 may be of the singleacting type, and cylinder 66, rather thanbeing of the free piston type as above described, may also be providedwith a piston rod, as shown by the dashed line 140 in FIG. 3, whichactuates another single-acting pilot valve, as shown by the dashed line142. With this arrangement, the single-acting pilot valve 76 would beemployed in the case ofjackknifing to the right, as above described, andthe single-acting pilot valve 142 would be employed in the caseofjackknifing to the left.

Referring now to FIGS. 4, 5 and 6, one form of fifth wheel mechanismusable in the system of FIG. 1 is shown. Here, front end 143 ofsemitrailer 12 has a plate 144 suitably secured to its bottom surface146 to which kingpin 148 is secured. A somewhat conventional fifthwheelplate 150 is provided having the usual rearwardly opening slot 152therein terminating in a semicircular forward end which receives kingpin148. Kingpin 148 has a locking slot 152 formed therein which is engagedby a conventional locking mechanism, as shown by the dashed lines 154 inFIG. 5. Fifth wheelplate 150 has gear 64 secured thereto which drivesrack 62, as above described. Fifth wheelplate 150 and gear 64 arerotatably mounted on a member 156 by means of shaft 158 and suitablethrust bearings 160. Member 156 is in turn mounted for rocking movementon rear end 162 of tractor 10 by means of suitable trunnions 164supported by conventional pillow blocks 166 mounted on tractor 10. Plate144 on semitrailer 12 has a block 168 which is received in slot 152 infifth wheelplate and thus causes fifth wheelplate 150 and gear 64 toturn with semitrailer 12.

Referring now to FIG. 7, an airbrake system for the tractorsemitrailer10, 12 is schematically shown, generally indicated at 170. Here, aconventional air pump 172 supplies air to reservoir 174 which, in turn,is coupled to master brake valve 176. Master brake valve 176 is actuatedby conventional brake pedal 178. Master brake valve 176 is coupled bylines 180, 182 to the tractor brakes 22, as shown. Thus, in conventionalfashion, actuation of brake pedal 178 actuates master brake valve 176 toapply air pressure from air reservoir 174 through air lines 180, 182 totractor brakes 22. Master brake valve 176 has a conventional airdischarge port 184 and thus, upon deactuation of brake pedal 178, masterbrake valve 176 bleeds the air from the tractor brakes 22 thereby torelease the same.

Another air line 186, including the conventional hose connection 188,couples master brake valve 176 to the trailer brakes 26 so thatactuation of brake pedal 178 likewise causes master brake valve 176 toapply air pressure through air line 186 to apply trailer brakes 26,release of brake pedal 178 causing master brake valve 176 to bleed theair pressure from the trailer brakes. It will be understood that the airbrake system 170, above described, is conventional, and has been shownand described in its most rudimentary form.

Another air line 190 is coupled to air reservoir 174, and is coupled bysolenoid valve 192 to antijackknife pilot valve 76. Solenoid valve 192is actuated to couple air line 190 to antijackknife pilot valve 76 by asuitable switch 194 which may be manually actuated by the driver, asshown by the dashed lines 196 and/or actuated by a suitable speedresponsive device as shown by the dashed lines 198. Thus, in certaininstallations, it may be desirable to have the antijackknife systemnormally operative at all times, but to permit the operator to disablethe system for close-in maneuvering of the tractor-semitrailer byactuation of manual switch 196, thereby to actuate solenoid valve 192 soas to disable pilot valve 76. In other installations, it may bedesirable to have the antijackknife system normally disabled, so as topermit normal maneuvering of the tractor-semitrailer, and to enable theantijackknife system in response to speed responsive device 98, such asfor example when the tractor-semitrailer reaches a speed of about 20miles per hour.

In the specific embodiment, antijackknife pilot valve 76 is coupled toactuate both tractor brake relief valve 200 and trailer brake boostervalve 202. Tractor brake relief valve 200 is coupled to air lines 180,182 and is provided with a discharge port 204. Thus, actuation oftractor brake release valve 200 by pilot valve 76 will bleed air fromthe tractor brakes 22, thus to decrease the braking effort applied bythe tractor brakes, despite the fact that the driver may be actuatingbrake pedal 178.

Air line 206 is connected to air line 190 and is coupled by trailerbrake booster valve 202 to the trailer brake air line 186. Thus, uponactuation of trailer brake booster valve 202 by pilot valve 76, trailerbrakes 26 are applied, even though the driver may not at the time beactuating brake pedal 178. On the other hand, if the driver is actuatingbrake pedal 178 so that master brake valve 176 applies air to thetrailer brakes 26, actuation of the trailer brake booster valve 202 willapply additional air pressure to the trailer brakes 26 thereby to applyadditional braking effort thereto. It will readily be understood thatthe pilot valve 76, tractor brake relief valve 200 and trailer brakebooster valve 202 are of the modulating type, i.e., progressiveactuation of pilot valve 76 by progressive movement of piston rod 74 ineither direction away from the neutral position of piston 72 of cylinder68 will progressively apply increased actuating air pressure to therelief valve 200 and booster valve 202, and in turn causing those valvesprogressively to decrease the braking effort applied by the tractorbrakes 22 and to increase the braking effort applied by the trailerbrakes 26, respectively. It will be readily understood that if separatesingle-acting pilot valves 76, 142 are emloyed, as above described, suchvalves would merely be coupled in parallel between solenoid valve 192and release and booster valves 200, 202. Further, while employment ofboth the tractor brake relief valve 200 and trailer brake booster valve202 is illustrated, and is considered to be preferred, it will beunderstood that either relief valve 200 or booster valve 202 may beeliminated in any given installation.

Referring now to FIG. 8, in which like elements are indicated by likereference numerals, and in which comparable elements are indicated bythe same reference numeral with the suffix piston 36' of cylinder 32' iscoupled to front wheel 16 for linear movement in either direction awayfrom its neutral position in response to turning of the front wheels 16in either direction away from their centered position. Thus, with frontwheels 16 centered, as shown, piston 36' is in its centered position, asshown in solid lines, and with front wheels 16 turned toward the right,as shown by the arrow 210, piston 36' is moved toward end 1 of cylinder32', as shown by the dashed lines at 360. Piston 56' of cylinder 52' hasits piston rod 60' coupled for actuation in response to pivotal turningmovement of trailer 12 with respect to tractor 10. When the trailer 12is centered with respect to tractor 10, piston 56' is in its neutralposition, as shown in solid lines. With trailer 12 pivotally movingtoward the right, as shown by the arrow 126, piston 56 is moved towardend 112' of cylinder 52 as shown by the dashed lines at 56a.

Cylinder 68' has its piston 72' connected to piston rod 74' which isconnected to actuate antijackknife pilot valve 76 (FIG. 1). Fluidconduit 86' connects ends 110' of cylinder 32', 84', of cylinder 68, and90 of cylinder 52. Fluid conduit 92' connects ends 94' of cylinder 32',114' of cylinder 68' and 1 l2 ofcylinder 52'.

In this embodiment, each cylinder 32', 6B and 52' has fluid therein onboth sides of its respective pistons 36', 72' and 56. Thus, spaces 98',100' and 102' respectively on one side of pistons 36', 72 and 56',together with fluid conduit 86', are filled with suitable hydraulicfluid, thus forming a first closed fluid system, and spaces 104, 106 and108' on the other side of pistons 36', 72' and 56, together with fluidconduit 92, are likewise filled with suitable hydraulic fluid, thusforming a second closed fluid system.

It will now be readily seen that functionally the antijackknife system28' of FIG. 8 operates in the same manner as the system 28 of FIG. 1.Thus, with wheels 16 being in the centered position as shown, pivotalmovement of semitrailer 12 toward the right, as shown by the arrow 126,will result in movement of piston 56 of cylinder 52' toward the left, asshown by arrow 212. The fluid in the thus reduced space 108' is forcedthrough fluid conduit 92 into space 106 causing piston 72' and pistonrod 74' to move toward the left, as shown by the arrow 2M, thereby toactuate antijackknife pilot valve 76. This leftward movement of piston72' of cylinder 86' is possible since the fluid in the thus reducedspace 100' is forced through fluid conduit 86' into and accommodated bythe increased space 102 of cylinder 52'. It will be readily seen thatthe system functions in the identical manner in the case of jackknifingto the left.

lt will be readily understood that while simplified rack and pinionarrangements 42, 46 and 62, 64 have been shown for actuating pistons 34,36 of cylinders 30, 32, and pistons 54, 5 6 of cylinders 50, 52, otherlinkages may equally advantageously be employed for actuating therespective pistons.

While there have been described above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of the invention.

What is claimed is:

i. In combination with a wheeled tractor vehicle having selectivelyactuable wheel brakes and steerable front wheels, a wheeled semitrailervehicle having selectively actuable wheel brakes, means for pivotallycoupling said semitrailer to said tractor, and means for normallyselectively applying said tractor and semitrailer brakes; anantijackknifing system comprising: means for sensing the absence of anormal coordinated relationship between the steered position of saidfront wheels and the pivotal position of said semitrailer wit respect tosaid tractor, said normal relationship occurring when said tractor andsemitrailer are normally traveling a highway; and means for modifyingthe braking effort applied by at least one of said tractor andsemitrailer brakes in response to said sensing means thereby to assistthe driver in restoring said normal relationship.

2. The system of claim 1 wherein said modifying means increases thebraking effort applied by said trailer brakes in response to saidsensing means.

3. The system of claim 1 wherein said modifying means decreases thebraking effort applied by said tractor brakes in response to saidsensing means.

4. The system of claim 3 wherein said modifying means furthersimultaneously increases the braking effort applied by said trailerbrakes in response to said sensing means.

5. The system of claim 1 wherein said sensing means includes first meansfor sensing turning movement of said front wheels in either direction,second means for sensing pivotal turning movement of said semitrailerwith respect to said tractor in either direction, and third meanscoupled to both of said first and second means and responsive theretofor sensing an uncoordinated turning movement of said front wheels withrespect to said semitrailer.

6. The system of claim 5 wherein said first means includes at least afirst fluid cylinder having fluid and a piston therein and means forlinearly actuating said piston in response to said turning movement ofsaid front wheels; said second means including at least a second fluidcylinder having fluid and a piston therein and means for linearlyactuating said piston in response to said turning movement of saidsemitrailer; said third means including at least a third fluid cylinderhaving fluid and a piston therein, and fluid conduit means for couplingsaid first, second and third cylinders in a closed fluid system wherebymovement of said piston of one of said first and second cylinders in theabsence of corresponding coordinated movement of said piston of theother of said first and second cylinders causes movement of said pistonof said third cylinder thereby to accommodate the fluid displaced bymovement of said piston of said one cylinder; said modifying means beingcoupled to said piston of said third cylinder and actuated thereby inresponse to movement thereof.

7. The system of claim 6 wherein said piston of said third cylinder isin a neutral position in response to said normal relationship, saidpiston of said third cylinder being moved toward one end thereof inresponse to uncoordinated turning movement of said semitrailer withrespect to said front wheels in one direction, and toward the other endthereof in response to uncoordinated turning movement in the oppositedirection, said modifying means being actuated in response to movementof said piston of said third cylinder in either direction away from saidneutral position.

8. The system of claim 7 wherein said modifying means includes firstauxiliary means for selectively decreasing the braking effort applied bysaid tractor brakes, second auxiliary means for selectively increasingthe braking effort applied by said trailer brakes, and actuator meanscoupled to said piston of said third cylinder for actuating said firstand second auxiliary means.

9. The system of claim 8 wherein said tractor and semitrailer brakes areair actuated, said first auxiliary means comprising a first valve forbleeding air from said tractor brakes, said second auxiliary meanscomprising a second valve for increasing the air pressure applied tosaid trailer brakes, said actuator means comprising a pilot valvecoupled to said first and second valves for actuating the same.

10. The system of claim 5 wherein said first means includes a first pairof first and second fluid cylinders each having fluid and a pistontherein, means for coupling said pistons of said first and secondcylinders for simultaneous movement, and

means for linearly simultaneously actuating said pistons of said firstand second cylinders in response to said turning movement of said frontwheels; said second means including a second pair of third and fourthfluid cylinders each having fluid and a piston therein, means forcoupling said pistons of said third and fourth cylinders forsimultaneous movement, and means for linearly simultaneously actuatingsaid pistons of said third and fourth cylinders in response to saidturning movement of said semitrailer; said third means including a thirdpair of fifth and sixth cylinders each having fluid and a pistontherein, and first fluid conduit means for coupling said first, thirdand fifth cylinders in a first closed fluid system and second fluidconduit means for coupling said second, fourth and sixth cylinders in asecond closed fluid system whereby movement of the pistons of one ofsaid first and second pairs of cylinders in the absence of correspondingcoordinated movement of the pistons of the other of said first andsecond pairs of cylinders causes movement of the pistons of said thirdpair of cylinders thereby to accommodate the fluid respectivelydisplaced by movement of the pistons of said one pair of cylinders, saidmodifying means being coupled to the piston of at least one of saidthird pair of cylinders and actuated thereby in response to movementthereof.

11. The system of claim 10 wherein said fifth and sixth cylindersrespectively have spring means therein for urging the respective pistonsin a direction to discharge fluid therefrom.

12. The system of claim 11 wherein said modifying means includes firstauxiliary means for selectively decreasing the braking efi'ort appliedby said tractor brakes, second auxiliary means for selectivelyincreasing the braking effort applied by said trailer brakes, saidpistons of said third pair of cylinders respectively having a neutralposition in response to said normal relationship, one of said third pairof cylinders being of the free piston type, and actuator means coupledto said piston of the other of said third pair of cylinders and to saidfirst and second auxiliary means for actuating the same in response tomovement of said last-named piston in either direction away from itsneutral position.

13. The system of claim 11 wherein said modifying means includes firstauxiliary means for selectively decreasing the braking effort applied bysaid tractor brakes, second auxiliary means for selectively increasingthe braking effort applied by said trailer brakes, said pistons of saidthird pair of cylinders respectively having a neutral position inresponse to said normal relationship, said piston of said fifth cylinderbeing moved toward one end thereof against the force exerted by therespective spring means in response to uncoordinated turning movement ofsaid semitrailer with respect to said front wheels in one direction,said piston of said sixth cylinder being moved toward one end thereofagainst the force exerted by the respective spring means in response touncoordinated turning movement in the opposite direction, first actuatormeans coupled to said piston of said fifth cylinder and to said firstand second auxiliary means for actuating the same in response to saiduncoordinated turning movement in said one direction, and secondactuator means coupled to said piston of said sixth cylinder and to saidfirst and second auxiliary means for actuating the same in response tosaid uncoordinated turning movement in said opposite direction.

14. The system of claim 5 wherein said first means includes a firstfluid cylinder having a piston therein with fluid respectively on theopposite sides thereof and means for linearly actuating said piston inresponse to said turning movement of said front wheels; said secondmeans including a second fluid cylinder having a piston therein withfluid respectively on the opposite sides thereof and means for linearlyactuating said piston in response to said turning movement of saidsemitrailer; said third means including a third fluid cylinder having apiston therein with fluid respectively on opposite sides thereof, andfirst fluid conduit means for coupling said first, second and thirdcylinders on one side of the respective pistons in a first closed fluidsystem and second fluid conduit means for cou ling said first, secondand third cylinders on the other side of he respective pistons in asecond closed fluid system whereby movement of said piston of one ofsaid first and second cylinders in the absence of correspondingcoordinated movement of said piston of the other of said first andsecond cylinders causes movement of said piston of said third cylinderthereby to accommodate the fluid displaced by movement of said piston ofsaid one cylinder; said modifying means being coupled to said piston ofsaid third cylinder and actuated thereby in response to movementthereof.

15. The system of claim 1 further comprising means for selectivelyenabling and disabling said antijackknifing system.

16. The system of claim 15 wherein said last-named means includes speedresponsive means for enabling said antijackknifing system in response toa predetermined speed of said trailer and semitrailer.

1. In combination with a wheeled tractor vehicle having selectivelyactuable wheel brakes and steerable front wheels, a wheeled seMitrailervehicle having selectively actuable wheel brakes, means for pivotallycoupling said semitrailer to said tractor, and means for normallyselectively applying said tractor and semitrailer brakes; anantijackknifing system comprising: means for sensing the absence of anormal coordinated relationship between the steered position of saidfront wheels and the pivotal position of said semitrailer with respectto said tractor, said normal relationship occurring when said tractorand semitrailer are normally traveling a highway; and means formodifying the braking effort applied by at least one of said tractor andsemitrailer brakes in response to said sensing means thereby to assistthe driver in restoring said normal relationship.
 2. The system of claim1 wherein said modifying means increases the braking effort applied bysaid trailer brakes in response to said sensing means.
 3. The system ofclaim 1 wherein said modifying means decreases the braking effortapplied by said tractor brakes in response to said sensing means.
 4. Thesystem of claim 3 wherein said modifying means further simultaneouslyincreases the braking effort applied by said trailer brakes in responseto said sensing means.
 5. The system of claim 1 wherein said sensingmeans includes first means for sensing turning movement of said frontwheels in either direction, second means for sensing pivotal turningmovement of said semitrailer with respect to said tractor in eitherdirection, and third means coupled to both of said first and secondmeans and responsive thereto for sensing an uncoordinated turningmovement of said front wheels with respect to said semitrailer.
 6. Thesystem of claim 5 wherein said first means includes at least a firstfluid cylinder having fluid and a piston therein and means for linearlyactuating said piston in response to said turning movement of said frontwheels; said second means including at least a second fluid cylinderhaving fluid and a piston therein and means for linearly actuating saidpiston in response to said turning movement of said semitrailer; saidthird means including at least a third fluid cylinder having fluid and apiston therein, and fluid conduit means for coupling said first, secondand third cylinders in a closed fluid system whereby movement of saidpiston of one of said first and second cylinders in the absence ofcorresponding coordinated movement of said piston of the other of saidfirst and second cylinders causes movement of said piston of said thirdcylinder thereby to accommodate the fluid displaced by movement of saidpiston of said one cylinder; said modifying means being coupled to saidpiston of said third cylinder and actuated thereby in response tomovement thereof.
 7. The system of claim 6 wherein said piston of saidthird cylinder is in a neutral position in response to said normalrelationship, said piston of said third cylinder being moved toward oneend thereof in response to uncoordinated turning movement of saidsemitrailer with respect to said front wheels in one direction, andtoward the other end thereof in response to uncoordinated turningmovement in the opposite direction, said modifying means being actuatedin response to movement of said piston of said third cylinder in eitherdirection away from said neutral position.
 8. The system of claim 7wherein said modifying means includes first auxiliary means forselectively decreasing the braking effort applied by said tractorbrakes, second auxiliary means for selectively increasing the brakingeffort applied by said trailer brakes, and actuator means coupled tosaid piston of said third cylinder for actuating said first and secondauxiliary means.
 9. The system of claim 8 wherein said tractor andsemitrailer brakes are air actuated, said first auxiliary meanscomprising a first valve for bleeding air from said tractor brakes, saidsecond auxiliary means comprising a second valve for increasing the airpressure applied to said trailer brakes, said actuator means Comprisinga pilot valve coupled to said first and second valves for actuating thesame.
 10. The system of claim 5 wherein said first means includes afirst pair of first and second fluid cylinders each having fluid and apiston therein, means for coupling said pistons of said first and secondcylinders for simultaneous movement, and means for linearlysimultaneously actuating said pistons of said first and second cylindersin response to said turning movement of said front wheels; said secondmeans including a second pair of third and fourth fluid cylinders eachhaving fluid and a piston therein, means for coupling said pistons ofsaid third and fourth cylinders for simultaneous movement, and means forlinearly simultaneously actuating said pistons of said third and fourthcylinders in response to said turning movement of said semitrailer; saidthird means including a third pair of fifth and sixth cylinders eachhaving fluid and a piston therein, and first fluid conduit means forcoupling said first, third and fifth cylinders in a first closed fluidsystem and second fluid conduit means for coupling said second, fourthand sixth cylinders in a second closed fluid system whereby movement ofthe pistons of one of said first and second pairs of cylinders in theabsence of corresponding coordinated movement of the pistons of theother of said first and second pairs of cylinders causes movement of thepistons of said third pair of cylinders thereby to accommodate the fluidrespectively displaced by movement of the pistons of said one pair ofcylinders, said modifying means being coupled to the piston of at leastone of said third pair of cylinders and actuated thereby in response tomovement thereof.
 11. The system of claim 10 wherein said fifth andsixth cylinders respectively have spring means therein for urging therespective pistons in a direction to discharge fluid therefrom.
 12. Thesystem of claim 11 wherein said modifying means includes first auxiliarymeans for selectively decreasing the braking effort applied by saidtractor brakes, second auxiliary means for selectively increasing thebraking effort applied by said trailer brakes, said pistons of saidthird pair of cylinders respectively having a neutral position inresponse to said normal relationship, one of said third pair ofcylinders being of the free piston type, and actuator means coupled tosaid piston of the other of said third pair of cylinders and to saidfirst and second auxiliary means for actuating the same in response tomovement of said last-named piston in either direction away from itsneutral position.
 13. The system of claim 11 wherein said modifyingmeans includes first auxiliary means for selectively decreasing thebraking effort applied by said tractor brakes, second auxiliary meansfor selectively increasing the braking effort applied by said trailerbrakes, said pistons of said third pair of cylinders respectively havinga neutral position in response to said normal relationship, said pistonof said fifth cylinder being moved toward one end thereof against theforce exerted by the respective spring means in response touncoordinated turning movement of said semitrailer with respect to saidfront wheels in one direction, said piston of said sixth cylinder beingmoved toward one end thereof against the force exerted by the respectivespring means in response to uncoordinated turning movement in theopposite direction, first actuator means coupled to said piston of saidfifth cylinder and to said first and second auxiliary means foractuating the same in response to said uncoordinated turning movement insaid one direction, and second actuator means coupled to said piston ofsaid sixth cylinder and to said first and second auxiliary means foractuating the same in response to said uncoordinated turning movement insaid opposite direction.
 14. The system of claim 5 wherein said firstmeans includes a first fluid cylinder having a piston therein with fluidrespectively on the opposite sides thereof and means for linearlyactuating said piston in response to said turning movement of said frontwheels; said second means including a second fluid cylinder having apiston therein with fluid respectively on the opposite sides thereof andmeans for linearly actuating said piston in response to said turningmovement of said semitrailer; said third means including a third fluidcylinder having a piston therein with fluid respectively on oppositesides thereof, and first fluid conduit means for coupling said first,second and third cylinders on one side of the respective pistons in afirst closed fluid system and second fluid conduit means for couplingsaid first, second and third cylinders on the other side of therespective pistons in a second closed fluid system whereby movement ofsaid piston of one of said first and second cylinders in the absence ofcorresponding coordinated movement of said piston of the other of saidfirst and second cylinders causes movement of said piston of said thirdcylinder thereby to accommodate the fluid displaced by movement of saidpiston of said one cylinder; said modifying means being coupled to saidpiston of said third cylinder and actuated thereby in response tomovement thereof.
 15. The system of claim 1 further comprising means forselectively enabling and disabling said antijackknifing system.
 16. Thesystem of claim 15 wherein said last-named means includes speedresponsive means for enabling said antijackknifing system in response toa predetermined speed of said trailer and semitrailer.